The present invention relates to disc brakes for vehicles, and in particular to air-operated disc brakes for commercial vehicles with an internal actuator which is displaced to apply the brake. Specifically, the present invention is directed to an apparatus and method for quick, reliable indication of the amount of stroke of an internal actuator of an air disc brake.
Pneumatically-operated disc brakes have been undergoing development and deployment on commercial vehicles since at least the 1970's, and are beginning to replace drum-style brakes due to advantages in areas such as cooling, fade resistance and serviceability. German patent publication DE 40 32886 A1, and in particular FIG. 1 of this document, discloses an example of such an air disc brake mechanism. In this design, a pneumatic diaphragm chamber 12 is attached to a rear face of the disc brake caliper housing 3, and applies a brake actuation force through a linear actuator rod 10 to a brake actuator lever 9 within the caliper. The brake's actuator lever in turn transfers and multiplies, via an eccentric, the force applied by the actuator rod to one or more spindles 14 which force brake pads 20 against a brake disc 1.
Notwithstanding the advantages of air-operated disc brakes, a disadvantage of brakes with internal actuator levers contained within a caliper housing and/or attached pneumatic housing is the lack of convenient means to assess the amount of remaining brake capacity, and specifically, to assess whether there remains a sufficient amount of actuator lever stroke (travel) in order to permit full application of the brake. This is particularly a problem where rapid assessment of brake condition is desired, such as during a pre-journey inspection or at a government safety inspection station.
Providing a reliable and convenient indication of internal actuator stroke is hampered by brake design constraints, such as a general lack of available space in the axle/wheel/brake envelope for external mounting of internal actuator stroke sensing devices, and the undesired exposure of equipment extending outward from the brake caliper, which subjects such equipment to harsh environmental conditions and potential physical damage from, for example, road debris. Accordingly, determining whether the brake actuator has sufficient stroke left to provide adequate braking force requires extensive, time-consuming vehicle and/or brake disassembly, typically including wheel removal to permit access to the brake caliper for inspection. This lack of a convenient actuator stroke indicator and resulting maintenance and inspection burden is a factor in the wide-spread market adoption of pneumatically-operated disc brake technology. Thus, at least for cost and vehicle safety requirement compliance reasons, it would be highly desirable to be able to have an easily accessed, reliable external indication of an air disc brake's remaining actuator stoke.
In view of the foregoing, it is an object of the present invention to provide a disc brake actuator stroke indicator and method to permit rapid, convenient actuator stroke determination without significant brake disassembly. This and other objects of the invention are achieved by the placement of an actuator stroke indicator coupled to the actuator assembly in an access port of the disc brake caliper housing, where the port is small enough to avoid compromising caliper housing integrity. The actuator stroke indicator may be, for example, a simple mechanical indicator readable immediately outside the caliper housing, or an electrical sensor, such as a potentiometer, coupled to a remotely-readable actuator stroke indicator display. A further embodiment of an electrical sensor arrangement would place the remotely-readable actuator stroke indicator display at a vehicle operator's position to permit operator monitoring of actuator stroke without leaving the operator's compartment.
The present invention's approach to providing actuator stroke indication has the advantages of avoiding compromise of caliper housing structural integrity by avoiding the need for large viewing access holes, providing easily accessible and reliable stroke indication, providing an indicator that is well within the available brake/wheel/hub space envelope, and providing a stroke indicator that is well shielded from adverse environmental conditions and physical damage from road debris. In addition, remote display of actuator stroke would permit a vehicle operator to monitor actuator stroke or receive actuator stroke limit warnings directly at the operator's position in the vehicle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.